In many diagnostic and therapeutic decisions in medicine, the appropriate course of action is the one which maximizes a measurable quantity such as life expectancy. In these situations, analytic approaches to decision making may be preferable to the traditional approach based on clinical judgement. We aim to promote the use of analytic approaches by developing techniques for the solution of a number of decision problems and by implementing these techniques on computer. We will select decision problems which apply to large numbers of patients, especially those at high risk for having disease or complications of therapy, and which are amenable to a quantitative approach. We will consider both diagnostic and therapeutic problems. Our methods will involve the development of decision trees and mathematical models to manipulate available data bases. We will implement on computer a number of the mathematical models developed to solve specific problems. This will allow whole classes of related problems to be solved rapidly, and will facilitate access to and use of our methods by both the clinician and the health care planner. We will provide answers to the decision problems considered, or if existing data is insufficient for a definitive solution, we will identify specific areas in which data collection is needed or institute data collection of our own. We will also develop interactive educational computer programs based on simplified versions of some of our analyses. Education of medical students and physicians in the techniques of formal decision analysis is essential if the medical community is to understand and accept their use.